Question about Garmin Edge 830

Should fit. Unfortunately, I had already bought a suitable mount before the 830. But there was also one in the box that would have fitted.

I use my Edge 830 for road bike (standard mount) and MTB (purchased, slightly longer MTB mount).
The mount in the standard package would also have fit on my MTB handlebars. There is enough clearance for various common handlebar thicknesses.